Last spring and summer, huge protests set off by corruption scandals engulfed two Central American nations. In Guatemala, an investigation led by a United Nations-sponsored International Commission Against Impunity exposed a far-reaching customs corruption ring and uncovered evidence that its leader was none other than the country’s president, Otto Pérez Molina. Protests in Guatemala City grew, and in September, Mr. Pérez Molina resigned and was sent to jail to await trial.

In Honduras, protests erupted when a local journalist revealed that millions of dollars of public funds from the country’s health care system had been funneled to the ruling National Party and the election campaign of President Juan Orlando Hernández. A handful of administrators and business executives have been indicted for other corruption in the health system, but no charges have been brought against Mr. Hernández or other top party officials over the diversion of funds to the party. Thousands of torch-bearing protesters demanded Mr. Hernández’s resignation and a United Nations-backed commission like Guatemala’s.

In response, Mr. Hernández convened a tightly controlled “national dialogue,” in which many opposition leaders refused to participate, and then proposed a government-sponsored investigative body with no autonomy. When this failed to placate protesters, the Organization of American States (OAS) stepped in to help design an alternative plan. The result was the Support Mission Against Corruption and Impunity in Honduras.

The mission was inaugurated at the OAS headquarters in Washington last month amid much fanfare and a ringing endorsement from the State Department. A department spokesman, John Kirby, said the mission “responds to the legitimate demands of the Honduran people for vigorous and meaningful action against corruption.”

Opponents in Honduras, however, have denounced the plan as toothless and are insisting on an independent, United Nations-backed body — and 54 members of Congress have urged Secretary of State John Kerry to support their demand. A coalition of almost all the country’s human rights groups declared that the new mission was “limited in its ability to attack corruption and impunity in the country.”

Unlike the Guatemalan commission, which has a strong record of fighting organized crime and high-level corruption, the Honduran one won’t directly participate in investigations and prosecutions. Instead, its international team of judges and lawyers will merely provide technical support to local investigators and prosecutors who are part of the judiciary and susceptible to political pressure. The mission can make recommendations for reforming the broken justice system, but the government is free to ignore them.

Honduras needs help. Its extreme levels of violence, among the highest in the world, go hand in hand with an appalling rate of criminal impunity. The country’s security forces are heavily infiltrated by organized crime — “rotten to the core,” a former police official told The Miami Herald. Two weeks later, the official was shot dead. Scores of journalists, lawyers, land rights activists, gay rights advocates and opposition figures have been assassinated, without consequence for their killers.

Whether the mission can achieve anything will depend on whether there is sufficient political will. There is little cause for optimism: Mr. Hernández and the National Party have a record of running roughshod over the rule of law.

In 2012, as president of Congress, Mr. Hernández ousted several Supreme Court justices and illegally stacked the bench with his allies. In 2014, his party dissolved a widely respected independent police reform commission without enacting its recommendations. And the Honduran attorney general, Oscar Chinchilla, has so far failed to investigate or prosecute National Party leaders in the diversion of health care funds to party accounts.

Sadly, the American government is ill positioned to offer help. In 2009, the State Department under Secretary Hillary Clinton helped a military coup in Honduras succeed by blocking efforts to restore the left-leaning president, Manuel Zelaya, to power. Since then, Washington’s diplomatic efforts have focused on shoring up a series of corrupt post-coup governments. More than 100 members of Congress have called on the Obama administration to condemn human rights violations by security forces, and have questioned America’s security assistance to Honduras.

Yet Washington continues to back Mr. Hernández. At the height of last year’s protests, the American ambassador to Honduras proclaimed that “relations between the United States and Honduras are perhaps the best in history.” This year, the United States government has again increased military and police support to Central America, with Honduras receiving a significant percentage of those funds, much of it through the opaque Central America Regional Security Initiative.

Given the limits of the anti-corruption mission’s mandate and the allegations against senior officials involved in carrying out its recommendations, it seems unlikely that this body will overcome the crisis in Honduras. Instead, it seems intended to give a veneer of respectability to Washington’s continued support for the Hernández regime.

Still, the appropriations legislation in Congress for 2016 does provide tools to pressure the Honduran government. It makes half of the assistance to Honduras — amounting to tens of millions of dollars — conditional on State Department certification that the authorities are taking effective steps to combat corruption, cooperate with commissions against impunity, and investigate and prosecute “members of military and police forces who are credibly alleged to have violated human rights.”

But is the State Department willing to take the certification process seriously? This is something many members of Congress have had serious questions about in recent years. Congressional oversight may be the only guarantee that due diligence is done.

Protesters will doubtless continue to march through the streets of Tegucigalpa — as they did last month — calling for a more effective United Nations-backed anti-corruption body. If the OAS-sponsored mission fails to deliver results, Mr. Hernández could get another dose of people power like the one that brought down Guatemala’s president.

Alexander Main is Senior Associate for International Policy at the Center for Economic and Policy Research.